NOTES ON COMMITTING TO EMACS'S REPOSITORY    -*- outline -*-

* Commit metainformation

** Commit in the author's name

If installing changes written by someone else, commit them in their
name, not yours.

** Commit message format

Commit messages should follow the conventions used in all modern
distributed version-control systems. That is, they should consist of

- A self-contained topic line, preferably no more than 75 chars long.

- If other content follows the topic line, there should be a blank
  line separating the two.

- Follow the blank line with ChangeLog-like entries for the specific
  changes you made, if any.  (As long as Emacs maintains ChangeLog
  files, just copy the entries you made in them to the commit message
  after the blank line.)

- Preferred form for several entries with the same content:

   * help.el (view-lossage):
   * kmacro.el (kmacro-edit-lossage):
   * edmacro.el (edit-kbd-macro): Fix docstring, lossage is now 300 keys.

  (Rather than anything involving "ditto" and suchlike.)

** Unnecessary metainformation

There is no need to make separate change log entries for files such as
NEWS, MAINTAINERS, and FOR-RELEASE, or to indicate regeneration of
files such as 'configure'.  "There is no need" means you don't have
to, but you can if you want to.

* Commit to the right branch

Development normally takes places on the trunk.
Sometimes specialized features are developed on separate branches
before possibly being merged to the trunk.

Development is discussed on the emacs-devel mailing list.

Sometime before the release of a new major version of Emacs
a "feature freeze" is imposed on the trunk.  No new features may be
added after this point.  This is usually some months before the release.

Shortly before the release, a release branch is created, and the
trunk is then free for development.

For example, "emacs-23" for Emacs 23.2 and later, "EMACS_23_1_RC" for
23.1, "EMACS_22_BASE" for 22.x, and "EMACS_21_1_RC" for 21.x.

Consult emacs-devel for exactly what kinds of changes are allowed
on what branch at any time.

** elpa

This branch does not contain a copy of Emacs, but of the Emacs Lisp
package archive (elpa.gnu.org).  See admin/notes/elpa for further
explanation, and the README file in the branch for usage
instructions.

* Install changes only on one branch, let them get merged elsewhere if needed.

In particular, install bug-fixes only on the release branch (if there
is one) and let them get synced to the trunk; do not install them by
hand on the trunk as well.  E.g. if there is an active "emacs-24" branch
and you have a bug-fix appropriate for the next emacs-24.x release,
install it only on the emacs-24 branch, not on the trunk as well.

Installing things manually into more than one branch makes merges more
difficult.

http://lists.gnu.org/archive/html/emacs-devel/2010-03/msg01124.html

The exception is, if you know that the change will be difficult to
merge to the trunk (eg because the trunk code has changed a lot).
In that case, it's helpful if you can apply the change to both trunk
and branch yourself (when committing the branch change, indicate
in the commit log that it should not be merged to the trunk, by
including the phrase "Not to be merged to master", or any other phrase
that matches "merge").

* Installing changes from your personal branches.

If your branch has only a single commit, or many different real
commits, it is fine to do a merge.  If your branch has only a very
small number of "real" commits, but several "merge from trunks", it is
preferred that you take your branch's diff, apply it to the trunk, and
commit directly, not merge.  This keeps the history cleaner.

In general, when working on some feature in a separate branch, it is
preferable not to merge from trunk until you are done with the
feature.  Unless you really need some change that was done on the
trunk while you were developing on the branch, you don't really need
those merges; just merge once, when you are done with the feature, and
Bazaar will take care of the rest.  Bazaar is much better in this than
CVS, so interim merges are unnecessary.

Or use shelves; or rebase; or do something else.  See the thread for
yet another fun excursion into the exciting world of version control.

http://lists.gnu.org/archive/html/emacs-devel/2010-04/msg00086.html

* Installing changes from gnulib

Some of the files in Emacs are copied from gnulib.  To synchronize
these files from the version of gnulib that you have checked out into
a sibling directory of your branch, type "admin/merge-gnulib"; this
will check out the latest version of gnulib if there is no sibling
directory already.  It is a good idea to run "git status" afterwards,
so that if a gnulib module added a file, you can record the new file
using "git add".  After synchronizing from gnulib, do a "make" in the
usual way.

To change the set of gnulib modules, change the GNULIB_MODULES
variable in admin/merge-gnulib before running it.

If you remove a gnulib module, or if a gnulib module
removes a file, then remove the corresponding files by hand.

* Backporting a bug-fix from the trunk to a branch (e.g. "emacs-24").

Indicate in the commit log that there is no need to merge the commit
to the trunk, e.g. start the commit message with "Backport:".  This is
helpful for the person merging the release branch to the trunk.

http://lists.gnu.org/archive/html/emacs-devel/2010-05/msg00262.html

* How to merge changes from emacs-24 to trunk

[The section on git merge procedure has not yet been written]

Inspect the change log entries (e.g. in case too many entries have been
included or whitespace between entries needs fixing). If someone made
multiple change log entries on different days in the branch, you may
wish to collapse them all to a single entry for that author in the
trunk (because in the trunk they all appear under the same date).
Obviously, if there are multiple changes to the same file by different
authors, don't break the logical ordering in doing this.

You may see conflicts in autoload md5sums in comments.  Strictly
speaking, the right thing to do is merge everything else, resolve the
conflict by choosing either the trunk or branch version, then run
`make -C lisp autoloads' to update the md5sums to the correct trunk
value before committing.

* Re-adding a file that has been removed from the repository

Let's suppose you've done:

git rm file; git commit -a

You can just restore a copy of the file and then re-add it;
git does not have per-file history so this will not harm
anything.

Alternatively, you can do

git revert XXXXX

where XXXXX is the hash of the commit in which file was removed.
This backs out the entire changeset the deletion was part of,
which is often more appropriate.

* Undoing a commit (uncommitting)

If you have not pushed the commit, you may be able to use `git reset
--hard' with a hash argument to revert the your local repo copy to the
pre-commit state.

If you have pushed  commit, resetting will be ineffective because it
will only vanish the commit in your local copy.  Instead, use `git
revert', giving it the commit ID as argument. This will create a
new commit that backs out the change. Then push that.

Note that git will generate a log message for the revert that includes
a git hash.  Please edit this to refer to the commit by the first line
of its log comment, or by committer and date, or by something else
that is not the hash.  As noted previously, it is best to avoid hashes
in comments in case we someday have to change version-control systems
again.

* Bisecting

This is a semi-automated way to find the revision that introduced a bug.
Browse `git help bisect' for technical instructions.
